Sufficient evidence exists to say that more than one-half the earth's population is undernourished or malnourished. The great contrasts in world levels of food and nutrition are here illustrated in eight tables summarizing relevant data from national food balance sheets and dietary surveys. In critical areas (Asia and the Far East, Near East, Africa and Latin America), prevalence of disease involving nutritional deficiencies can be directly related with poor food supplies. Generally, (a) diets show satisfactory energy content, though there are periodic serious calorie shortages in some areas; (b) food supplies are too rich in carbohydrate, and too poor in nutrients essential to good health; (c) this can be corrected only by consumption of protective foods like pulses, milk, meat, eggs and fish. The specific role of fish in diets is discussed. Regional variations in fish consumption are shown. Although fish contributes only a small percentage to total calorie intake, it has a great potential use in the relief of protein malnutrition which is the most serious nutrition problem in the critical areas. Calcium intake from fish is generally unimportant except in a few countries. Limited data are provided which indicate that fish could provide more thiamine and riboflavin than at present. Only a few countries obtain substantial fat intake from fish, but even lesser intakes are considered to be of interest. Estimates are given of percentage increases of food required to make even limited nutritional improvement in average diets over 25 years, taking into account the fast increasing populations. The figures for fish are: 90 per cent generally, 120 per cent for Asia and the Far East, 130 per cent for the Near East. Five references are given.